1. Field of the Invention
The present invention generally relates to a heat exchanger for exchanging heat between two fluids, for example, between a refrigeration medium and air or the like, and more particularly, to a fin tube heat exchanger for use in an air conditioner, a refrigerator or the like.
2. Description of the Prior Art
Recently, air conditioners tend to be reduced in size or to be thin. A fin tube heat exchanger is occasionally employed in the air conditioner, and therefore, there has been an increased demand for higher performance thereof.
FIGS. 1 and 2 illustrate one of the conventional fin tube heat exchangers.
A plate-shaped fin, generally shown by 1, is provided with a plurality of fin collars 2 extending from a fin base and spaced from each other at regular intervals and a plurality of raised pieces 1a formed between the collars 2 on the same face of the fin base as the fin collars 2 are formed. The raised pieces 1a extend from the base plate up to the same height to prevent a temperature boundary layer from growing. A plurality of openings are defined between the fin base and the raised pieces 1a to permit an air flow A to pass therethrough. A plurality of heat exchanger tubes 3 extend through the fin collars 2 and are enlarged so as to be rigidly secured therein. Two tubes 3 are coupled to each other in the form of a figure "U" through a bend. When the air flow A passes between the tubes 3, an area 4a or 4b called "dead water region" upon which the air flow A hardly exerts any influence appears behind each tube 3 in a direction of the air flow A.
In the above described construction, all the raised pieces 1a are of the same configuration and are aligned in several rows in the direction of the air flow A. Accordingly, since the distance between adjacent raised pieces 1a is relatively small, they exert less influence upon the temperature boundary layer. Furthermore, leg portions of the raised pieces 1a are formed in a direction normal to a front edge of the fin 1. Because of this, the raised pieces 1a neither change the direction of the air flow A nor effectively turn it into turbulent flow. Thus, the dead water regions 4a and 4b become large and this fact reduces an effective heat transfer area. Since the leg portions of the raised pieces 1a are formed one behind another in the direction of the air flow A, resistance against the flow is concentrated, with the result that it is impossible to uniformly distribute the velocity of air flow A. The aforementioned conventional fin tube heat exchanger is, therefore, disadvantageous in that the raised pieces 1a can not be effectively utilized.